Conventionally, a magnetic sensor, combining Hall elements and a magnetic substance (magnetic flux concentrator) with a magnetic amplification function, has been known. For example, Patent Document 1 relates to a magnetic field direction detection sensor, which enables detecting a direction of a magnetic field in three dimensions and comprises a magnetic flux concentrator, having a flat shape, and Hall elements, positioned at end regions of the magnetic flux concentrator.
This arrangement provides effects of enabling, by means of the magnetic flux concentrator, a horizontal magnetic field to be detected and the magnetic field to be amplified at regions at which the Hall elements are present.
A magnetic sensor combining Hall elements can be integrated, because Hall elements are not positioned at end regions of a permanent magnet but disposed at rotational axis regions at which horizontal components of a magnetic field are maximized by the effect of a magnetic flux concentrator.
FIG. 1 is an arrangement diagram for describing the conventional magnetic sensor (see Patent Document 1), and in the figure, 1 indicates a semiconductor substrate, 2a and 2b indicate Hall elements, 3 indicates a buffer coat layer, 4 indicates a base layer, and 5 indicates a magnetic flux concentrator.
FIG. 2 is a process diagram for describing a method for manufacturing the magnetic flux concentrator of the conventional magnetic sensor and shows a process of adhering a magnetic tape onto a semiconductor substrate 11. First, an IC (Integrated Circuit)-processed wafer is prepared. Next, using an epoxy adhesive, the magnetic tape (amorphous metal tape) is adhered onto the wafer. A magnetic flux focusing pattern 14 is then formed by photolithography. Etching of the amorphous metal is then performed. The magnetic flux concentrator is thus formed on the semiconductor substrate 11. Here, a central position of a magnetic sensing surface of each Hall element is positioned near a circumferential edge of the magnetic flux concentrator. Also here, the magnetic flux concentrator has a film thickness of no less than 20 μm. The magnetic flux concentrator is prepared by processing a thick magnetic tape by wet etching. In this case, the epoxy adhesive is approximately 2 to 4 μm thick, and a distance from a magnetic sensing surface of each Hall element to a bottom surface of the magnetic flux concentrator is approximately 6 to 8 μm. Also in this case, the magnetic flux concentrator 5 is 15 μm thick. Furthermore, an angle formed by a top surface of the semiconductor substrate 1 and a side surface of the magnetic flux concentrator 5 is substantially 90°.
Patent Document 2 relates to a magnetic sensor, including a magnetic flux concentrator, with a magnetic amplification function, which detects magnetic flux, leaking from an end of the magnetic flux concentrator, by semiconductor Hall elements.
And with this arrangement, after forming the semiconductor Hall elements, the magnetic flux concentrator is formed by depositing a soft magnetic thin film by electroplating. And a two-layer structure is formed by depositing a Ti thin film, which is a first metal film, to 0.05 μm by sputtering, thereafter using a dry film resist to form a pattern corresponding to a magnetic substance in a form of an opening, and depositing a Ni—Fe alloy thin film, which is a second metal film, to 0.07 μm.
The Ti thin film that is the first metal film is adopted for improving close adhesion of a basing insulating layer and the Ni—Fe alloy thin film.
In this manufacturing method, the magnetic sensor including the Hall elements and the magnetic flux concentrator formed of the soft magnetic material can be manufactured compactly and readily by a manufacturing method compatible with an LSI (Large Scale Integrated circuit) manufacturing process. Furthermore, the magnetic sensor can be made high sensitivity by shortening a distance between the semiconductor Hall elements and the magnetic flux concentrator.
With the arrangement using the magnetic tape as the magnetic flux concentrator, there is a problem in that a large stress is generated at the Hall elements below the tape due to the tape being adhered onto the semiconductor substrate using the epoxy adhesive. Also when the magnetic tape is used, it is impossible to control the thickness of the magnetic substance.
Furthermore with the magnetic sensor shown in FIG. 1, because the adhesive used between the semiconductor circuit 1 and the magnetic flux concentrator 5 shrinks upon hardening, a high tensile force is applied to the wafer and the wafer becomes warped as a whole. When the adhesive is applied more thickly, the adhesive force increases, but the sensitivity decreases, more shrinkage occurs, and it is difficult to process and form the coated adhesive thinly and uniformly. Also, when the adhesive is applied thinly, although the adhesive force becomes weaker, the adhesive layer being made thin improves the sensor sensitivity.
It was thus difficult to improve the sensitivity and reduce variations of the sensitivity while maintaining the adhesive force (relaxing the stress) and taking into consideration the thickness of the adhesive.
Also conventionally, the thickness of the adhesive is set to 2 to 4 μm from the standpoint of obtaining a predetermined sensitivity, and this thickness of the adhesive cannot be kept uniform readily. Consequently, the distance from the magnetic sensing surface of each Hall element to the bottom surface of the magnetic flux concentrator in the conventional magnetic sensor must be restricted to no more than 6 to 8 μm, and it is difficult to suppress variations of the sensitivity while maintaining this distance.
In a case of using the manufacturing method described in Patent Document 2 to manufacture the magnetic sensor with the arrangement shown in FIG. 1, because the base metal layer and the magnetic flux concentrator contact the semiconductor substrate across the same area, a stress applied to the Hall elements and a mounted IC becomes large and this consequently causes generation of an offset voltage.
However, if the areas of contact with the semiconductor substrate are made small by reducing the areas of the magnetic substance and the base metal layer, positional shifts of the magnetic substance cause magnetic flux density variations at the regions at which the Hall elements are present and magnetic saturation is quickened. Therefore, the magnetic substance and the base metal layer are required to have areas of a certain size or more.
Furthermore, in the case of the magnetic sensor thus manufactured, the metal film with the two-layer structure is stacked between the semiconductor substrate and the magnetic flux concentrator by stacking the Ti thin film, which is the first metal film, to 0.05 μm by sputtering and thereafter depositing the Ni—Fe alloy thin film, which is the second metal film, to 0.07 μm. However, the Ti thin film that is the first metal layer is provided to improve close adhesion of the basing insulating layer and the Ni—Fe alloy thin film and no consideration whatsoever is made in regard to the coefficient of thermal expansions of the two metal films and the magnetic flux concentrator. Therefore, magnetostriction occurs due to the thermal expansion difference between the NiFe in the magnetic flux concentrator 5 and the Ti, W, or TiW alloy in the metal film, and the magnetic characteristics of the magnetic sensor that combines the Hall elements and the magnetic substance are consequently unstable.
Furthermore, in the case of the magnetic sensor shown in FIG. 1, because the central position of the magnetic sensing surface of each Hall element is positioned near the circumferential edge of the magnetic flux concentrator, diameter variations and positional shifts within a horizontal plane of the magnetic flux concentrator cause large variations of the sensitivity along the X-axis and Y-axis, and the unbalance of the sensitivity along the X-axis and Y-axis and a sensitivity along a Z-axis.
The above-mentioned patent documents do not make any statements in particular in regard to the distance from the magnetic sensing surface of each Hall element to the bottom surface of the magnetic flux concentrator, and this distance is guessed to be approximately 6 to 8 μm in consideration of adhesive force, processability, sensitivity, and variations of the sensitivity.
As another problem, with the magnetic sensor shown in FIG. 1, because the angle formed by the top surface of the semiconductor substrate 1 and the side surface of the magnetic flux concentrator 5 is substantially 90°, a perpendicular side surface of the magnetic flux concentrator is positioned very close to each Hall element, although the magnetic flux concentrates at the side surface and thereby improves the magnetic detection function. However the magnetic flux concentrates excessively, magnetic saturation occurs and it becomes difficult to secure linearity of sensor output.
The present invention has been made in view of the above issues, and an object thereof is to provide a magnetic sensor, which combines Hall elements and a magnetic substance having a magnetic amplification function, and with which extremely stable magnetic characteristics are realized by consideration of an area of contact of a base layer of the magnetic substance and a semiconductor substrate, and a method for manufacturing the magnetic sensor.
Another object of the present invention is to provide a magnetic sensor, with which control of thickness of the magnetic substance is enabled to prevent generation of a large stress in the Hall element, and a method for manufacturing the magnetic sensor.
Yet another object of the present invention is to provide a magnetic sensor, with which extremely stable magnetic characteristics are realized by provision of a metal film with a two-layer structure between the semiconductor substrate and the magnetic substance, and a method for manufacturing the magnetic sensor.
Yet another object of the present invention is to provide a two-dimensional or a three-dimensional magnetic sensor, which combines Hall elements and a magnetic substance, having a magnetic amplification function, and with which a central position of a magnetic detecting surface of each Hall element is disposed inward from an end of the magnetic substance by just a predetermined distance and sensitivity variations along an X-axis and Y-axis and sensitivity variations along a Z-axis are controlled, a three-dimensional magnetic sensor, with which a sensitivity along the X-axis and Y-axis and a sensitivity along the Z-axis are well-balanced, and a method for manufacturing these magnetic sensors.
Yet another object of the present invention is to provide a magnetic sensor, with which variations of the sensitivity are suppressed by consideration of a distance between each Hall element and the magnetic substance, and a method for manufacturing the magnetic sensor.
Yet another object of the present invention is to provide a magnetic sensor, with which a side surface of the magnetic substance has a tapered shape and linearity can be secured without improving sensitivity or lowering sensitivity by consideration of a degree of concentration of magnetic flux onto the magnetic substance and consideration of magnetic saturation, and a method for manufacturing the magnetic sensor.    Patent Document 1: Japanese Patent Laid-Open No. 2002-71381    Patent Document 2: Japanese Patent Laid-Open No. 2003-142752